Patent GB-538594-A (GB)
Title: Improvements in tractors
IPC: B62D49/06
Filed: 1939-12-05
Abstract: 538,594. Variable-speed and reversing gearing. DYKES, W. V. (Bonham Manufacturing Co.). Dec. 5, 1939, No. 31503. [Class 80 (ii)] [Also in Groups XXXI and XXXII] The driving shaft of a tractor drives each of the right- and left-hand driving means selectively and independently in either direction through a clutch unit mounted on said driving shaft, each clutch unit comprising a forward direct drive and an epicyclic reverse gear, the elements of the forward drive being independent of the elements of the reverse drive, the clutch units being selectively controlled to provide a forward or reverse drive for each driving means. The engine drives the four wheels through a clutch 29, two-speed gear 99, 101 provided with synchronizing friction wheels 106, 110, bevel gear 45, a central stub shaft 43. and two independent reversing gears 37 one for each side of the tractor. The reversing gears are controlled by the driver through reins (not shown) and levers 64 on independent cam shafts 63, so that the driving gears on each side can be independently set in the forward, reverse or free position. Each reversing gear comprises a multi-plate clutch 49 for the direct drive and an epicyclic train 68 for the reverse. The hub 48 of the clutch is keyed on the driving stub shaft 43 and the driven part 38 of the clutch is fixed to an end shaft 41 carrying a sprocket 42 driving the corresponding road wheel. The clutch is normally held engaged by springs 52 and is released by a cam on the corresponding shaft 63 acting through a ball-pivoted lever on the clutch-disengaging collar 54. A sun pinion 69 is keyed on each end of the driving shaft 43 and engages planet pinions 68 on a carrier 71 adapted to be held stationary by a brake band 73, the planet pinions also meshing with the toothed annulus 67 secured to the driven member 38 of the clutch. The brake is applied by means of a cam 83 on the shaft 63, this cam acting on a toggle lever 81 pivoted at 143. In order to set each cam shaft 63 in the three positions corresponding to forward, neutral, and reverse, a cam 86 provided on each shaft 63 is engaged by a roller 90, both rollers being mounted on a pin 89, on a yoke 87 which slides to and fro under control of a spring 95 and a dash-pot 93. In the neutral position shown in Fig. 5, the rollers 90 bear against recesses 130 in the cams 86 and hold the levers 64 vertical. If a lever, or a rein attached thereto, is pulled back slightly by the driver, as shown in Fig. 8 a nose 137 on the corresponding cam 86 forces the yoke 87 to the left, and if the lever is now released suddenly the clutch springs 52 acting on the cam shaft 63 rotate the shaft in the opposite direction, i.e. clockwise, the high point 135 on the cam 86 passing under the roller 90 before the dash-pot 93 allows the spring 95 to return the yoke to the right again. The corresponding cam shaft 63 is thus moved to the clutch-engaged position and the forward drive is engaged. When either lever is pulled back fully the cam shaft 63 is rotated sufficiently to apply the brake 73 and cause the reverse gear to be brought into action. Thus each side of the tractor can be driven forward or reverse or disengaged from the drive independently of the other side. The synchronizing device for the change-speed gear comprises bevelled friction wheel 106, 110 on the gear shafts 96, 101, their ratios being a mean between the ratios of the toothed gear trains. The wheel 106 is slidable on the shaft 96 and, when the gear is to be changed, is slid by a knob 108 into engagement with the wheel 110.